Concrete mixer



A. MOMILLAN CONCRETE MIXER May 25, 1948.

Filed Feb. 15, 1944 I am flndrewflc/llillan,

Patented May 25, 1948 CONCRETE MIXER Andrew 'McMillan, Milwaukee, Wis., assignor to.

Chain Belt Company, Milwaukee, Wis., a corporation of Wisconsin Application February 15, 1944, Serial No. 522,480

1 Claim.

The invention relates to concrete mixers, more especially those employed in the preparation of hydraulic cement concrete, and has for its principal object the mitigation or elimination of an obnoxious condition which, in prior apparatus of this character, normally attends the introduction of the aggregates and cement into the mixing chamber.

In the most widely used form of such machines the mixing chamber comprises apower driven drum mounted for rotation about a horizontal axis andhaving an axially disposed opening in each end wall and mixing blades of various form secured to its inner periphery. Measured quantitles of the aggregates, cement and water for producing batches of the concrete mixture are intermittently charged into the drum through one of said end openings, and after suitable agitation and mixing induced by rotation of the drum, the batches of mixed concrete are discharged through the other of said end openings.

The mixers may be stationary, as in the case of the well known central batching plants, or portable, of which the widely used paving and construction mixers are typical. In the stationary type charging of the dry aggregates is usually accomplished by chuting the materials through the charging opening of the drum from fixed bins or hoppers, while in the portable type the aggregates and cement are usually deposited in a power-driven charging skip positioned at or near the ground level, which skip is then elevated and tilted to discharge its contents through the drum charging-opening.

The hydraulic cement is a dry impalpable powder, readily dispersable in air, and since the charging and discharging openings of the drum in this type of mixer ordinarilyare not provided with closures, each time a batch of aggregates and cement is charged into the drum a cloud of cement-dust laden air is expelled therefrom, principally through the discharge opening. This air of course is not particularly suitable for breathing by the workmen and/or others in the vicinity, and furthermore the dust soon settles upon the machine and other adjacent objects where it forms an objectionable coating which hardens into a tenaciously adhering mass if hydrated by water from the job or from the atmosphere.

It is a primary object of this invention to substantially eliminate the emission of this dust cloud from the mixer, which object is accomplished by means of a liquid spray or curtain projected across at least the discharge opening of 2. the mixing drum. Preferably, although not necessarily, the liquid employed is a portion of the measured quantity of water which is to be introduced into the drum for mixing with the batch of dry aggregates and cement to form the concrete mixture.

Oneform of apparatus for attaining the above object is illustrated in the accompanying drawing forming a part of this specification, in which the, figure is a somewhat diagrammatic sectional-elevational View showing an installation for a well known paving type of mixer.

In the aid drawing, ii] indicates a conventiona1 mixer drum (with the internal mixing blades, the supports and the driving means therefor omitted) having a charging opening I l at one end anda discharging opening l2 at the other end. A charging skip, thethroat of which is shown at 53,. is adapted upon elevation and inclination to the position illustrated, to discharge a batch of aggregates and hydraulic cement into the drum in through the opening H. A Water tank I l, equipped with well known facilities (not shown) for filling the same, is provided for supplying the water for the mixture through a conduit which customarily enters the drum through the opening I substantially as shown. Flow of water through the conduit is controlled by a valve l6, and the tank is preferably provided with a well known form of adjustable mechanism (not shown but partially contained in an extension 14 of the tank) whereby the quantity of water supplied to the drum for each batch may be variably predetermined. All of the parts thus far mentioned may be of conventional types well known in the art.

For preventing, or at least materially reducing, the emission from the drum of the cement-dust cloud referred to above, one or more nozzles 26 are appropriately mounted adjacent at least the discharge opening l2. These nozzles may be of any suitable type, such for example as that disclosed in prior U. S. Patent No. 1,947,752 granted February 20, 1934, on an application filed by Alvin H. Benesh, which discharge liquid in a thin, fiat, laterally-spreading sheet. The nozzles are supplied with liquid by means of a pipe 2|, which may lead from any appropriate source of supply, but since the nozzles preferably discharge into the drum through the opening [2, and since present day practice requires accurate control of the quantity of water furnished for each batch of concrete, the pipe 2! preferably leads from the conduit I5 at or beyond the discharge side of the control valve it. Thus, the liquid discharged by the nozzles 20 is a portion of the predetermined quantity of water for each batch, and this quantity therefore need not be reduced to compensate for the liquid discharged from the nozzles. If

necessary, a pump 22 may be included in the line 5 2| to supply the liquid to the nozzles.

The nozzle or nozzles 20 are so disposed relative to the opening 12 as to provide a sheet or curtain 25 of liquid substantially completely shielding the 4 above disclosure except as may be required by the claim.

What is claimed is:

In a concrete mixer having a mixing chamber provided with a material-transfer opening, and means including a conduit having a control valve for supplying water for the mixture to the cham her, the combination of means for shielding said opening against the emission of dust theresaid opening against the emission of a dust .10 .through during charging of the dry constituents cloud therethrough, and any air-borne particles" which attempt to escape through the opening will versely of and through said opening into the chamber; and' liquid-supplying connections 'bebe washed down into the drum by the water, to

mingle with and become a part of the batch of concrete. The invention has proven quite effec- 15,

tive in the depressing of the heretofore unavoidable cement-dust cloud, since for best results in.

the mixing of concrete, it is common practiceto.

start water flow into the mixing drum slightly ahead of dry aggregate flow and to continue the 20 flow of water for a short period after all of the dry aggregate are charged into the drum,'thus, a water spray curtain may be maintained across the drum openings during the process of charging the drum with a'batch of dry aggregate. 5

While as above mentioned, experience shows that at least the major portion of the dust attempts'to escape through the discharge opening l2, forwhich reason the foregoing'description has been inlconnection with such opening, obvi- 3o ously asirriilar arrangement may be associated with the chargingjppe'ning ll if necessary or desirable. l

' Whilefo r purposesof disclosure one embodirn entiof the invention has been illustrated and 85 for the mixture into the chamber, comprising means jor discharging a curtain of liquid transtweensaid curtain discharging means and said water supply conduit of the mixer, said connecjtionscommunicating with said conduit inter- .mediate the discharge port of its control valve and the discharge port of the conduit.

McMILLAN.

REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED' STATES PATENTS- 

